The present invention relates to a shock sensor system and method, and in particular, it concerns a shock sensor configuration that enjoys significant reduction or elimination of field calibrations.
Shock sensors are used in many applications to monitor or detect shock forces imparted to an object that is fragile, under investigation, and/or of value. Additionally, shock sensors may be used to monitor security environments, such as glass surfaces, windows, and doors for example to indicate when a glass surface is tampered with or a shock is applied. Shock sensors as known in the art are frequently accelerometers utilizing sensing materials placed on a thin diaphragm with a proof mass attached to the diaphragm. Some of these devices also utilize materials having a piezoelectric effect. One frequent use of mechanical shock detection devices is in the field of indicator alarms. Such alarms include those for sensing movement, time, temperature and a number of other physical parameters. Examples of prior art are U.S. Pat. No. 6,737,979 to Smith et, al. and U.S. Pat. No. 5,612,670 to Snyder et al., whose disclosure is incorporated herein by reference.
Shock sensors are typically packaged in an inexpensive housing, frequently made of a range of plastic or other lower cost materials. Upon field installation of the sensor, the housing is attached to the surface and/or item to be monitored. In order to reduce cost, shock sensors are frequently manufactured with nominal electro-mechanical responses that cannot be substantially changed once the sensor is fabricated and subsequently field installed. In most cases, when the sensor, installed in its housing, together hereinbelow referred to in the specification and in the claims which follow as a “housing assembly”, a “sensor housing assembly”, and a “sensor configuration”, is field-installed as part of an alarm system, care must be taken to securely mount the housing assembly to the surface to be monitored.
Furthermore, the response of the housing assembly is very frequently calibrated upon installation, such as, but not limited to test shocks with an object of know mass to the surface on which the housing assembling is mounted, to ensure a repeatable shock response, so that the overall alarm system provides the desired sensitivity and/or robustness to fulfill its purpose. The term “field calibration” as used hereinbelow in the specification and in the claims which follows, is intended to mean primarily the installation calibration referred to in the previous sentence. The term “repeatable shock response”, as used in the specification and in the claims which follow, is intended to mean a consistent and repeatable response of the sensor housing, usually, but not always, a measure of the output signal of the shock sensor of the housing in response to test shocks applied to the surface upon which the housing is attached. Consistency and repeatability of the response is determined by any number of numerical and/or statistical techniques.
An exemplary shock sensor field calibration routine may be found in “New LIFEBOOK Series features Shock Sensor Utility Eco Power Saving Utility—White Paper”, Fujitsu-Siemens Computers, October 2007, pages 2 and 3, whose disclosure is incorporated by reference.
An example of a sensor configuration may be found in Snyder et al. in U.S. Pat. No. 5,612,670, whose disclosure is incorporated by reference. Snyder describes an aftermarket (i.e. retrofit) shock sensor configuration that may be used in automobiles. The configuration described comprises a configuration of circuits, inter alia, to give two separately adjustable thresholds to control overall sensor shock sensitivity. However, there is no discussion of details of the sensor housing assembly or of uniformity of its response to shocks.
The need for field calibrations brings with it concomitant expense, as such calibrations must be performed by individuals having a certain level of skill and attention. Qualified personnel, who are typically more highly-paid, are required for this type of work. Furthermore, additional instrumentation may also be needed for such field calibrations. Clearly, the time and expense related to field calibrations represents a significant cost component of an alarm system. If field calibrations for a sensor housing assembly may be reduced in scale or even eliminated, corresponding costs may be reduced for the system installer, and this cost reduction may also yield a lower price for the customer.
There is therefore a need for a shock sensor configuration with repeatable shock response that allows significant reduction and/or elimination of field calibrations.